AP CHEMISTRY UNIT 1 - Atomic structure and periodic trends
If a question asks you something like 'What is the outermost energy level that has electrons in element 2', you would respond with something like
n=
If there are 14.0 g of Si and 32.0 g of O present, what is the empirical formula of the compound?
Make sure you do ALL elements, don't skip one and be lazy. 14/28 = 1/2 and 32/16=2, so your coefficients are 1 and 4.
Which of the following correctly compares the atomic radius of F to that of O and provides the best explanation?
The atomic radius of F is smaller than that of O because F has a greater effective nuclear charge than O does.
Electronegativity is affected by two factors:
The smaller an atom, the more effectively its nuclear charge will be felt past its outermost energy level and the higher its electronegativity will be. The closer an element is to having a full energy level, the more likely it is to attract the necessary electrons to complete that level.
The decrease in the second ionization energy of alkali metals going down the group, as shown in the table above, can be best attributed to a decrease in the coulombic force of attraction due to
an increase in the average distance of the outermost electron from the nucleus.
Moving down a group, electronegativity _
decreases.
Electron affinity is like a
gun.
The height of the peaks correspond to the
# of e-.
What is Avogadro's number?
6.02 x 10²³ atoms per mole.
When asked how many valence electrons an element has that doesn't open the d shell, you must:
Combine s and p.
Binding energy is the same as
Ionization energy.
Atomic radius is like a
backwards gun.
Moving down a group, ionization energy _ because _
decreases because: Shells of electrons are added to the nucleus. Each inner shell shields the more distant shells from the nucleus, reducing the pull of the nucleus on the valence electrons and making them easier to remove. Protons are also being added, but the shielding effect of the negatively charged electron shells cancels out the added positive charge.
The second ionization energy is _ than the first ionization energy because _
greater because: When an electron has been removed from an atom, electron-electron repulsion decreases, and the remaining valence electrons move closer to the nucleus. This increases the attractive force between the electrons and the nucleus, increasing the ionization energy.
Electronegativity is like a
gun.
PES spectrums are read in order of
increasing to decreasing binding energy.
Anions are _ than atoms because _
larger because: When an electron is added to an atom, forming an anion, electron-electron repulsions increase causing the valence electrons to move farther apart, which increases the radius.
Electrons from which subshell of Cl will have the highest velocity after being ejected? 1s, 2p, 3p, or 3d?
3p, 3d doesn't exist for Cl. The farther an electron is from the nucleus, the lower its I.E., and the more K.E. it has after being ejected.
Explain why the 1st I.E. for Mg < the 1st I.E. for Al:
Aluminum is slightly smaller than Mg, and it has more protons than Mg. It also has more electrons, but since it is in the same period as Mg, there is no shielding effect. This means that Al has a greater ENC, making it harder to remove electrons from Al, thus resulting in Al have a higher I.E.
In ClO-, the negative charge in the ion is located around the oxygen atom. Why?
An oxygen atom is smaller than a chlorine atom and so it is more electronegative. This means that the electrons in the bond are more attracted to oxygen than chlorine. What you must do: Talk about size. REMEBER THIS. Talk about which is more electronegative. Talk about what being more electronegative means.
If you can be more specific when you talk about the heights of peaks in PES, do that. (Ex: if one has 2 e- and the other has 4e-, it's TWICE the height or HALF the height).
Ay ay captain.
When you're assigning elements to a table (ex: Element 1 is C, 2 is 0, 3 is P, ..) double check yourself and don't mess up, or you could ruin later answers.
Ay ay captain.
A sample of CaCO3 (molar mass 100. g) was reported as being 30. percent Ca. Assuming no calcium was present in any impurities, the percent of CaCO3 in the sample is _?
Ca has a molar mass of 40.078g 1. Create a simplified ratio of the molar mass of Ca and CaCO3 MassCa/MassCaCO3 = 40.078 g/100 g = 2/5 Simplified ratio: MassCa/MassCaCO3 = 2/5 *Note that we use 40.078x1 since there is only 1 mole Ca* 2. Isolate what you want, which is Mass CaCO3 MassCaCO3 = MassCa/(2/5) 3. Substitute what you're given in the problem We know that Ca was reported being 30%. 30% of 100 grams is 30. MassCaCO3 = 30g/(2/5) MassCaCO3 = 75 g 4. Divide what you calculated by the total molar mass of CaCO3 75g/100g = 75%
Which of the following best helps to account for the fact that the F- ion is smaller than the O2- ion?
F- has a larger nuclear charge than O2- has.
Mass number =
protons + neutrons (electrons don't count, their masses are negligible).
Cations are _ than atoms because _
smaller because: Generally, when electrons are removed from an atom to form a cation, the outer shell is lost, making the cation smaller than the atom. Also, when electrons are removed, electron-electron repulsions are reduced, allowing all of the remaining valence electrons to move closer to the nucleus.
When it comes to elements in the same period, the one with the higher EN is the _ one because _ _ are able to attract additional electrons because they have a higher _. When it comes to elements in the different groups, there is the same reasoning.
smaller, smaller atoms, ENC.
The primary exception to these trends are the electronegativity values for _, whose electronegativities are _
the 3 smallest noble gases, He, Ar, Ne, 0.
Approximately how many neutrons are present in a 10 g sample of argon atoms which has a mass number of 40?
If the mass # is 40, and Ar's atomic # is 18, 40-18=22, there are 22 neutrons. 10 g Ar (1 mol Ar/39.95 g Ar) (6.02e23 atoms Ar/1 mol Ar) (22 neutrons/1 atom Ar) = 3.3e24 You have to remember that there is a connection between number of atoms and moles.
How does the 1st I.E. of K compare to those of Ar and Cl?
It is less than both because a valence electron of K is farther from the nucleus than one of either Cl or Ar.
The I.E's for an element are listed below: 1st: 8 2nd: 15 3rd: 80 4th: 109 5th: 141 Which period 3 element is this element likely to be?
Mg. We see a jump between 2nd and 3rd. Mg will easily give away 1 to become Na, and then easily give away another to become Ne, which is a completely stable octet. But it won't give away a 3rd to because it already has achieved noble gas configuration.
Which of the following ions would have the most unpaired electrons? Mn2+, Ni3+, Ti2+, or Cr6+
Mn2+. These are all transition metals. Mn2+: [Ar]3d5 Ni3+: [Ar]3d7 Ti2+: [Ar]3d2 Cr6+: [Ar] D has 5 orbitals, according to Hund's rule, one electron will fill up each 5 orbitals before pairing up, therefore Mn has the most unpaired electrons.
The mass spectrum of an element is represented above. Which of the following is most likely the identity of the element?
Multiply all the masses (x-axis) by their relative abundances (y-axis) and add up those values to get your molar mass.
The effective nuclear charge experienced by the outermost electron of Na is different than the effective nuclear charge experienced by the outermost electron of Ne. This difference best accounts for which of the following?
Na has a lower first ionization energy than Ne.
The photoelectron spectra above show the energy required to remove a 1s electron from a nitrogen atom and from an oxygen atom. Which of the following statements best accounts for the peak in the upper spectrum being to the right of the peak in the lower spectrum?
Nitrogen atoms have a smaller nuclear charge than oxygen atoms.
Why do nonmetals have higher ionization energies than metals from the same period?
Nonmetals have higher ionization energies because they are closer to having filled a complete energy level.
When transition metals become ions, what subshell do they lose first?
S.
Ionization energy
The amount of energy required to remove an electron from an atom. Once an electron has been removed, the atom becomes a cation. The energy required to remove the next electron from the ion is called the second ionization energy, and so on. ex: P(g) -> P(g)+ + e-
The average mass in grams of one mole of carbon atoms is equal to
The average mass of a single carbon atom, measured in amus.
What can be inferred from examining mass spectroscopy data?
The existence of isotopes. Mass spectrometry is used to determine the masses for individual atoms of an element. Through mass spectrometry, it is proven that each element has more than one possible mass.
FRQ4: Explain the relative heights of the peaks when compared to one another.
The height of the peaks correspond to the number of electrons in each subshell. The s subshell's have 2 electrons and are the shortest. 2p has 6 electrons and is 3x taller than the s subshells. 3p has 4electrons and is 2x taller than the s subshells. - Talk about what height means - Talk about relation of heights
The mass spectrum shows the various isotopes of an element. The number of lines show _ , and the height of the lines show _ (ex: tallest line = most abundant isotope). The y-axis is _ and the x-axis is _. To calculate the average atomic mass of an element using the spectrum, you do _.
The number of isotopes, which ones are the most naturally occurring. Relative abundance %, mass number (in amu). (Mass # x relative abundance % in decimals) + (Mass # x relative abundance % in decimals) So if the relative % abundance is 30, you do x .30.
Which electrons would have the greatest velocity after ejection?
The one with the lowest binding/ionization energy.
Most transition metals share a common oxidation state of +2. Why?
Transition metals will lose their outermost s-block electrons when forming bonds.
FRQ3: Which element is # 3? Justify your answer using both properties.
*First thing you want to do is compare atomic radius sizes not I.E.'s* Chlorine. Element 3 has the 2nd largest radius. Cl and P have the largest radii of the 4 elements because they have 1 more outer shell than do C and O. Cl is smaller than P because it has more protons and thus a higher ENC, which pulls the electrons closer to the nucleus. *Great now you talked about 1 property, size, talk about the other* Additionally, Cl has a larger ionization energy than P (element 2) because it has more protons and is smaller, thus it has a higher ENC and it would be harder to remove an electron from it than for P.
The s subshell has _ orbital(s). The p subshell has _ orbital(s). The d subshell has _ orbital(s). The f subshell has _ orbital(s).
1 3 5 7
When hafnium metal is heated in an atmosphere of chlorine gas, the product of the reaction is found to contain 62.2 percent Hf by mass and 37.4 percent Cl by mass. What is the empirical formula for this compound?
1. Divide the percentages by the molar masses of their respective elements 62.2/molar mass Hf = x 37.4/molar mass Cl = y 2. Whichever is the smaller number of x and y, divide both x and y by that number (ex: lets say x is the smallest number) x/x=1, y/x=3 These are your coefficients. What if you get a fraction? Say x/x=1 and y/x=1/2 Scale it up: Your coefficients would then be 2 and 1
FRQ4: Explain the reason for 3 discrete areas of ionization energies.
Each discrete area of I.E. represents a different energy level. The distance of the e- from the nucleus determines the I.E. of the electrons, and every energy level is a different distance from the nucleus. Sulfur has 3 energy levels, so 3 discrete areas. -Talk about how each area = energy level -Distances from nucleus = diff I.E.
FRQ4: Justify there being 5 peaks.
Each peak represents a subshell of sulfur. Sulfur has 5 subshells, 1s, 2s, 3s, 2p, and 3p. Each subshell are different distances from the nucleus and thus have different I.E'S. -Talk about subshells - Distances from nucleus = diff I.E.
Transition metals don't have 4s23d4 or 4s23d9. They rather go to 3d5 or 3d10, so they take one electron from the s orbital to make 4s13d5 or 4s13d10.
Ex: Cr electron configuration is not 4s23d4, it is 4s13d5.
READ CAREFULLY: Which atom that contains only one electron in the highest occupied energy sublevel? This question is not asking you to pick the element with the highest occupied sublevel (ex: 5d vs 2s), it is asking you to pick the element with only one electron in the highest occupied energy sublevel.
Oh okay, next time I'll read carefully and SLOWLY.
Of C, O, P and Cl, which element would have the highest electronegativity?
You could answer with either O or Cl. Cl: Electronegativity increases as an energy level comes close to being full so Cl has the highest E.N. (is to attract the necessary electrons to complete that level). O: Electronegativity increases as atomic radius decreases (greater ENC), so it is expected that O would have the highest E.N.
HOW TO SOLVE: A student determines that an unknown compound contains 49 percent C by mass. Which of the following could be the compound?
You look at all the diagrams, count the number of C's, multiply the number of C's by the mass of C (12.01) to get the total mass of C in the compound. Then you divide that number by the total mass of the entire compound, and you see if it is 49%.
Moving left to right across a period, atomic radius _ because _
decreases because: Protons are added to the nucleus, so the valence electrons are more strongly attracted to the nucleus, decreasing the atomic radius. Electrons are also being added, but they are all in the same shell and about the same distance from the nucleus, so there is not much of a shielding effect.
You won't be asked about electron affinity, but if you are, follow the same trends as _
electronegativity.
Moving left to right across a period, ionization energy _ because _
increases because: Protons are added to the nucleus, which increases its positive charge. The electrons being added are all in the same energy level at about the same distance from the nucleus, so they do not effectively shield these added protons. For this reason, the negatively charged valence electrons are more strongly attracted to the nucleus, which increases the energy required to remove them.
Moving down a group, atomic radius _ because _
increases because: Shells of electrons are added to the nucleus. Each shell shields the more distant shells from the nucleus and the valence electrons get farther away from the nucleus. Protons are also being added, but the shielding effect of the negatively charged electrons cancels out the added positive charge.
As electrons are removed, ionization energy gradually _ until the shell is empty, then makes _ _ _ because _
increases, then makes a big jump because: When the valence shell is empty, the next electron must come from a shell that is much closer to the nucleus, making the ionization energy for that electron much larger than for the previous ones(ex: For Na, the 2nd I.E. is much larger than the 1st. For Mg, the 1st and 2nd I.E.'s are comparable but the 3rd is much larger than the 2nd).
Moving left to right across a period, electronegativity _
increases.
Atomic number is the number of
protons.
Electronegativity
A measure of the ability of the nucleus of an atom to attract other electrons in a bond.
How many unpaired electrons does sulfur have?
2. Why? It ends at 3p4. P has 3 orbitals. The first 3 electrons each fill one orbital, then the fourth electron pairs up with another electron. So two electrons are unpaired.
Nitrogen's electronegativity value is between those of phosphorus and oxygen. Which of the following correctly describes the relationship between the three values? C) The value for N is greater than that of P because N is smaller, but less than that of O because N has a smaller effective nuclear charge. D) The value for N is greater than that of P because N has fewer electrons, but less than that of O because N is smaller.
C) N only has 2 shells of electrons, while P has 3, making N smaller and more able to attract additional electrons, meaning a higher electronegativity. N and O both has 2 shells, but O has more protons and a higher ENC, thus O has the higher EN. Also for D, N is not smaller than O.
Explain why the 1st and 2nd I.E.'s for Ca are comparable but the 3rd I.E. is much greater:
Calcium will easily get rid of its first two electrons in order to achieve noble gas configuration. However, it be much harder to get rid of a third electron because it is already in a stable form, which is why the 3rd I.E. is greater.
The four species above have the same electron configuration. Which of the following statements correctly identifies the species with the largest radius and provides an explanation based on Coulomb's law? Cl-, Ar, K+, Ca2+
Cl−, because its nuclear charge exerts the least attractive force on the electrons in the 3p sublevel. According to Coulomb's law, the radius of the atom or ion depends on the strength of attraction of the nuclear charge for the outer electrons. The greater the attraction, the smaller the radius. The attractive force exerted by the nucleus on an electron in the 3p sublevel increases with increasing charge of the nucleus (or with increasing number of protons). Cl−Cl- has the smallest number of protons among the species listed, and therefore the largest radius.
The average atomic mass of an element (amu) measures the average mass of a mole of atoms of that element in grams, as well as he average mass of a single atom of that element in amus.
For example, if one carbon atom has a mass of 12 amu, then 1 mole of carbon atoms has a mass of 12 grams.
Explain why the 1st I.E. for Mg > the 1st I.E. for Ca:
Mg is smaller than Ca because it has one less energy level and thus the electrons are closer to the nucleus than they are in Ca. This means Mg has a greater ENC than Ca, making it harder to remove electrons from Mg, thus resulting in Mg have a higher I.E. - Always got to connect it back to the prompt.
Does the negative or positive charge of an ion affect the mass spectrum?
No. The only subatomic particles that contribute to the mass of any atom are neutrons and protons. Changing the number of electrons, whether you add them or take them away, does not change the mass significantly.
In general, do metals or nonmetals from the same period have higher ionization energies? Why?
Nonmetals have higher ionization energies because they are closer to having filled a complete energy level.
Why does an ion of phosporus have a larger radius than a neutral atom of phosphorus?
The electrons in a phosphorus ion have greater coulombic repulsion than those in the neutral atom.
Electron affinity
The energy change that occurs when an electron is acquired by a neutral atom in its gaseous state. Exothermic process. Ex: P(g) + e- -> P-(g)
